1. Field in the Industry
The present invention concerns parts of electronic devices made of ferritic free cutting stainless steel.
2. Prior Art
The pro of precision parts, for which high accuracy in sizes as well as corrosion resistance are required, includes machining of material ferritic stainless steel such as SUS430 to which 0.2% or more of S is added for the purpose of improving machinability. This kind of ferritic free cutting stainless steel part is made by machining after being treated by passivation for improving corrosion resistance thereof. The passivation is usually carried out by immersing the parts in warmed nitric acid for a predetermined period of time.
Many of the electronic parts contains metals such as Ag, Cu and Al as the components of circuits. These metals tend to be corroded by sulfides such as H.sub.2 S, which may be in the atmosphere, and the corrosion causes trouble of abnormal working of the electronic apparatus. Such trouble has been experienced in apparatus in which ferritic free cutting stainless steel parts are incorporated. The cause of the trouble is considered to be corrosion by generation of gaseous compounds containing sulfur (usually called "sulfide gases") from the parts of ferritic free cutting stainless steel, which received machining and passivation treatment.